Conventional USB connectors provide a predetermined voltage and have a relatively low output power. With the increased electric power of electrical equipment which are powered or charged by USB ports, the USB promoter group established the USB Power Delivery Specification (USB PD) in July 2012, according to which USB ports can provide electric power with a maximum value equal to 100 W. USB connectors are widely used by customers. There are so many various products with a USB connector, such as mobile phones, chargers, lamps, electric fans, computers, portable hard disks, automobiles, routers, and the like. After establishment of the USB power delivery specification for high-power transfer, the USB connector will play a role in electric tools with electric power below 100 W. Moreover, with the development of electrical intelligence applications and the Internet of Things, electric tools can have a USB connector for supporting high power transfer in accordance with the USB Power Delivery Specification (USB PD) and other characteristics. This will greatly enhance a customer's experience and add to a product's features.